I know nothing about scientific computing, but I am sure you took a look at this,right?
http://sciruby.com/
It goes like: " Ruby has for some time had no equivalent to the beautifully constructed NumPy, SciPy, and matplotlib libraries for Python. We believe that the time for a Ruby science and visualization package has come..."
But status is pre-alpha, last commit 7 months ago... so dunno how much it can help...